Reference voltages available within an integrated circuit (IC) are typically temperature dependent. In order to provide a reliable and relatively constant reference voltage within the IC, the temperature dependent reference voltage is adjusted, or “trimmed.” The term “trimming” means to fine tune a selected parameter of a circuit. In the case of a temperature dependent reference voltage, trimming refers to fine tuning the value of the reference voltage that is output. The reference voltage is trimmed using a trimming circuit to achieve a particular result, for example, in compliance with a specification for the IC. Trimming is typically performed as part of the IC manufacturing and testing process prior to release and/or sale of the IC.
In some ICs, the trimming circuit operates by applying a selected amount of gain to the reference voltage to be trimmed using an amplifier. The amount of gain applied by the amplifier is determined at a particular temperature referred to as the “tuning temperature.” For example, the tuning temperature may be 0° C. While the reference voltage output from the tuning circuit is accurate at the tuning temperature, the reference voltage becomes less accurate as the temperature rises above the tuning temperature or falls below the tuning temperature.
For a selected temperature not equal to the tuning temperature, the amount of variance in the reference voltage compared to the desired value of the reference voltage per the specification increases with the magnitude of the difference between the selected temperature and the tuning temperature. For example, the difference between the reference voltage after trimming and the specification reference voltage is greater at a temperature of 120° C. than at 30° C. when the tuning temperature is 0° C. Even with trimming, the actual reference voltage may vary from the allowable range of the reference voltage per the specification to such a large extent that the reference voltage is no longer compliant with the specification of the IC. Such large variance in the reference voltage over the temperature range not only reduces operational efficiency of the IC, but also can result in reduced IC yield.
The present invention may address one or more of these issues.